Effect of temperature and aging duration on ethylene propylene diene monomer (EPDM) nonmetallic components used in caustic liquid waste transfer lines

Nonmetallic materials are used in waste transfer lines at the United States Department of Energy's Hanford Site Tank Farm in Benton County, Washington, USA. During use, the ethylene propylene diene monomer (EPDM) inner hose of the hose-in-hose transfer lines (HIHTLs) are exposed to beta and gamma radiation, caustic solutions as well as high temperatures and high pressures. Aging behavior of specimens of EPDM HIHTLs and dog-bone shaped specimens were evaluated by exposing to a solution of 25% sodium hydroxide (NaOH) at 38 degrees C, 54 degrees C and 77 degrees C for 6 and 12-months as well as water only at 77 degrees C for 12-months. Tensile strength and burst pressure of the specimens were characterized and compared with the unexposed (baseline) specimens. Both the tensile strength of the EPDM material and the burst pressure of the HIHTLs significantly decreased with the higher temperatures and longer exposure times. Analyses using scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS) of the HIHTLs and the dog-bone specimens were conducted. Results show that the surface degradation increased with increasing exposure temperature. Penetration of NaOH into the EPDM material also increased with increasing temperature and exposure duration.

Automated summary

The study revealed that the EPDM hoses experienced significant decreases in tensile strength and burst pressure under high temperatures and prolonged exposure, with surface degradation and increased penetration of NaOH into the material. Scanning electron microscopy analysis showed surface degradation increased with higher exposure temperatures.